Preparation method of high-temperature-resistant and solvent-resistant polyamide reverse osmosis composite membrane

Abstract

The invention discloses a method for preparing a high-temperature-resistant and solvent-resistant polyamide reverse osmosis composite membrane by an inorganic-organic coupling modification technology. More specifically, an inorganic nano-material and an ester compound containing silicon, aluminum, titanium and zirconium are introduced into a polyamide composite film forming system, so that the polyamide composite film shows better high temperature resistance and solvent resistance than a pure polyamide composite film.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of separation membrane materials, and relates to a method for preparing a reverse osmosis composite membrane, and in particular to a method for preparing a high-temperature-resistant and solvent-resistant polyamide (PA) reverse osmosis composite membrane. Background Art

[0002] Energy and environmental issues, including the safe water crisis, global warming, and shrinking energy supply, have been of great concern in recent years. So far, various technologies have been initially explored to obtain clean water, capture "greenhouse" gases, and find alternative energy sources. By solving some of the above-mentioned pressing problems, membrane separation has become one of the most important technologies. Membrane separation technology is becoming increasingly important in the separation industry and can be applied to the separation of various molecular weight components in the gas or liquid phase. The special advantage of membrane separation is that it does not require heating, so the energy usage is much lower than traditional thermal separation processes. Membrane separation includes microfiltration, ultrafiltration, nanofiltration and reverse osmosis. Reverse osmosis (RO) is currently the most widely used seawater desalination technology in the world. Compared with other technologies, it has higher efficiency and lower cost.

[0003] The performance of RO membranes depends largely on the membrane material and structure. Most commercial RO membranes are thin-film composites made from polymers with high mechanical, thermal, and chemical stability. Currently, composite membranes widely used in the water treatment industry primarily utilize interfacial polymerization, where a polyamide thin film is bonded to the surface of a microporous support membrane. The typical process is detailed in the groundbreaking U.S. Patent 4,277,344. First, polysulfone is coated onto a polyester nonwoven fabric to form a microporous support membrane. This is then immersed in an aqueous solution of diamine or polyamine. Excess amine solution is then removed from the membrane surface through air showering, roller pressing, and other methods. The membrane is then immersed in an organic, non-polar solution of polyacyl chlorides, where interfacial polymerization occurs with the chlorides, forming a dense, ultra-thin active layer of polyamide with separation properties. After membrane formation, thorough washing and appropriate heat curing can enhance membrane performance. The polysulfone base membrane material in polyamide composite membranes has a non-crosslinked linear structure, and the functional polyamide layer also has only a small proportion of crosslinked structures. Therefore, when treating wastewater containing organic solvents, especially polysulfone solvents such as amides, alkanones, and sulfoxides, the solvents swell the membrane, causing the base membrane pores to shrink significantly and destroying the structural integrity of the polyamide membrane, resulting in a rapid decline in water flux. When treating high-temperature wastewater, the high temperature significantly affects the membrane pore structure and chemical structure, resulting in a significant decline in membrane performance. This significantly limits the application range of polyamide composite membranes.

[0004] Therefore, there is an urgent need for energy-saving and environmentally friendly high-temperature and solvent-resistant separation membrane technology. Summary of the Invention

[0005] In response to the problem that the poor high-temperature and solvent resistance of reverse osmosis composite membranes limit their application scope, the present invention aims to propose a method for preparing a high-temperature and solvent-resistant polyamide reverse osmosis composite membrane; through this method, a coupling structure of inorganic nanomaterials and organic polymer matrix materials is introduced into the membrane layer, so that it exhibits better structural stability than pure polymer reverse osmosis membranes, while improving the hydrophilicity and pollution resistance of the membrane.

[0006] The present invention provides a method for preparing a high-temperature resistant and solvent-resistant polyamide reverse osmosis composite membrane, comprising the following steps: (1) Prepare a dimethylformamide (DMF) solution containing inorganic nanomaterials and polysulfone, and apply the solution to the surface of the non-woven fabric by a doctor blade or extrusion method to form a wet polysulfone film. After staying in the air for a period of time, it enters the coagulation tank of a pure water coagulation bath to form a porous polysulfone support membrane; (2) The porous polysulfone support membrane prepared in step (1) is contacted with an aqueous solution (aqueous phase) containing an inorganic nanomaterial and a monomer m-phenylenediamine; after removing the excess m-phenylenediamine solution on the surface of the porous polysulfone support membrane, the membrane is contacted with a xylene-n-hexane solution (organic phase) containing silicate, aluminate, titanate, zirconate compounds and the monomer trimesoyl chloride to perform an interfacial polymerization reaction to form a membrane containing a polyamide layer; the unreacted trimesoyl chloride solution on the surface of the membrane containing the polyamide layer is removed with excess n-hexane, and after curing and washing, a high-temperature resistant and solvent-resistant polyamide (PA) reverse osmosis composite membrane is obtained. In steps (1) and (2), the inorganic nanomaterials are independently selected from one or more of TiO2, La2O3, CeO2, MnO2, ZrO2, ZnO, SnO2, ZnS, CuS, FeS, Ag2S, CdS, C3N4 and their modified compounds. In step (1), in a dimethylformamide (DMF) solution containing an inorganic nanomaterial and polysulfone, polysulfone (PSF) is used as a membrane material, dimethylformamide (DMF) is used as a solvent, and the content of polysulfone (PSF) accounts for 13-19 wt% of the total amount of polysulfone and dimethylformamide; the amount of inorganic nanomaterial used is 0-5 wt% of the total amount of polysulfone and dimethylformamide. In step (2), in an aqueous solution containing an inorganic nanomaterial and a monomeric metaphenylenediamine, the concentration of metaphenylenediamine is 1.5-3.5 wt%. In step (2), in a xylene-n-hexane solution containing a silicate, an aluminate, a titanate, a zirconate, and a monomeric trimesoyl chloride, the concentration of trimesoyl chloride is 0.05-0.20 wt%, and the content of the ester compound is 0-0.5 wt%, preferably 0.001-0.15 wt%. The reaction is carried out in the solution for 5-60 s. In step (2), the curing temperature is 20-120°C and the curing time is 1-10 minutes.

[0007] This invention proposes a method for preparing a high-temperature and solvent-resistant polyamide reverse osmosis composite membrane. The polyamide (PA) thin layer is synthesized by interfacial polymerization of m-phenylenediamine and trimesoyl chloride. This method incorporates a coupled structure of inorganic nanomaterials and organic polymers into the membrane layer, resulting in superior structural stability compared to conventional reverse osmosis membranes and improving the composite membrane's solvent and high-temperature resistance. DETAILED DESCRIPTION

[0008] The following are preferred embodiments of the present invention, which are only used to explain the present invention and are not used to limit the present invention. Any related improvements made from this description fall within the scope of protection of the appended claims of the present invention: Preparation of inorganic-organic coupled polyamide reverse osmosis composite membrane: Preparation of supporting base membrane: 2.0 wt% TiO2 nanoparticles are dispersed in a casting solution containing 18 wt% polysulfone and 80% dimethylformamide, fully dissolved and degassed, and a microporous polysulfone base membrane with a total thickness of 140 microns after solidification is scraped on a non-woven fabric of about 100 microns at room temperature and room temperature pure water as a coagulation bath.

[0009] Preparation of aqueous monomer: 0.05 wt% TiO2 nanoparticles were dissolved and dispersed in an aqueous solution containing 3.0 wt% m-phenylenediamine.

[0010] Preparation of organic phase monomer solution: First, 0-5.0 wt% of the aforementioned ester compound is completely dissolved in xylene solvent, and then 1 part by weight of this solution is added to 9 parts by weight of anhydrous n-hexane solution containing 0.15 wt% of trimesoyl chloride to form a mixed monomer solution. After mixing, the ester content is 0-0.5 wt% and the acyl chloride content is 0.135 wt%.

[0011] Preparation of the composite membrane: The supporting base membrane was immersed in an aqueous monomer solution for 60 seconds, then removed to remove excess solution from the surface of the base membrane, blown with an air knife until the surface was semi-dry, and then contacted with an organic monomer solution for 30 seconds to form a membrane containing a polyamide layer; the unreacted trimesoyl chloride solution on the surface of the membrane containing the polyamide layer was removed with excess n-hexane, and then heat-treated for curing, washed, and rolled to obtain a polyamide reverse osmosis composite membrane.

[0012] Membrane performance test conditions: 25 ° C, 1000 ppm NaCl aqueous solution, 1.5 MPa pressure, 15% recovery rate test conditions (standard test conditions), after flushing for 30 minutes, the water flux and desalination rate are tested.

[0013] Membrane high-temperature and solvent resistance evaluation: After testing the membrane using the aforementioned standard test conditions, the membrane was subjected to continuous circulation for 24 hours using a 1.0 wt% DMF and 1000 ppm NaCl aqueous solution at 50°C, an operating pressure of 150 psi, and a recovery rate of 15%. The membrane was then re-circulated using standard test conditions and flushed for 30 minutes before testing for salt rejection and water flux.

[0014] Comparative Example: The ester content in the organic phase is 0, the initial membrane performance is a salt rejection rate of 99.3%, and a water flux of 1.35 M 3 / M 2 .d, after high temperature and solvent treatment, the desalination rate of NaCl was 94.1%, and the water flux was 0.43 M 3 / M 2 .d. Detailed results are shown in Table 1 Example

[0015] Tetraethyl silicate was used in the organic phase with a content of 0.02 wt %. Other conditions were the same as those of the comparative example. The results are listed in Table 1. The membrane performance was that the initial desalination rate of NaCl was 98.7% and the water flux was 1.44 M 3 / M 2 .d, after high temperature and solvent treatment, the desalination rate of NaCl was 95.2%, and the water flux was 1.12 M 3 / M 2 .d. Detailed results are shown in Table 1. Example

[0016] Other membrane preparation conditions were the same as those in Example 1, except that the content of tetraethyl silicate was 0.5 wt %. Other conditions were the same as those in the comparative example. The test conditions were the same as those in the comparative example. The membrane performance was that the initial desalination rate of NaCl was 89.3%, and the water flux was 2.12 M 3 / M 2 .d, after high temperature and solvent treatment, the desalination rate of NaCl was 91.2%, and the water flux was 1.98 M 3 / M 2 .d. Detailed results are shown in Table 1 Example

[0017] Tetrabutyl titanate was used in the organic phase with a content of 0.15 wt %. Other conditions were the same as those of the comparative example. The results are listed in Table 1. The membrane performance was that the initial rejection rate of NaCl was 99.1% and the water flux was 1.25 M 3 / M 2 .d, after high temperature and solvent treatment, the desalination rate of NaCl was 97.7%, and the water flux was 1.13 M 3 / M 2 .d. Detailed results are shown in Table 1. Example

[0018] Tetrabutyl titanate was used in the organic phase with a content of 0.50 wt %. Other test conditions were the same as those of the comparative example. The membrane performance was an initial NaCl rejection rate of 90.7% and a water flux of 2.07 M 3 / M 2 .d, after high temperature and solvent treatment, the desalination rate of NaCl was 94.2%, and the water flux was 1.88 M 3 / M 2 .d. Detailed results are shown in Table 1.

[0019] Examples 5-10 show the properties of composite membranes made from ester compounds of different types and contents, as shown in Table 1 for details.

Claims

1. A method for preparing a high-temperature resistant and solvent-resistant polyamide reverse osmosis composite membrane, characterized in that: The steps include: (1) Prepare a dimethylformamide (DMF) solution containing inorganic nanomaterials and polysulfone, and apply the solution to the surface of the non-woven fabric by a doctor blade or extrusion method to form a wet polysulfone film. After staying in the air for a period of time, it enters the coagulation tank of a pure water coagulation bath to form a porous polysulfone support membrane; (2) contacting the porous polysulfone support membrane containing inorganic nanomaterials prepared in step (1) with an aqueous solution (aqueous phase) containing inorganic nanomaterials and monomer m-phenylenediamine; after removing excess m-phenylenediamine solution on the surface of the porous polysulfone support membrane, reacting with a solution (organic phase) in which silicate, aluminate, titanate, zirconate compounds and monomer trimesoyl chloride are dissolved in a xylene-n-hexane mixed solvent to form a composite membrane containing a polyamide desalting layer; removing unreacted trimesoyl chloride solution on the surface of the membrane containing the polyamide layer with excess n-hexane, and obtaining a high-temperature resistant and solvent-resistant polyamide (PA) reverse osmosis composite membrane after curing treatment and washing.

2. The method for preparing a high-temperature resistant and solvent-resistant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: In step (1) and step (2), the inorganic nanomaterials are independently one or more of TiO2, La2O3, CeO2, MnO2, ZrO2, ZnO, SnO2, ZnS, CuS, FeS, Ag2S, CdS, C3N4 and modified compounds thereof.

3. The method for preparing a high temperature resistant and solvent resistant polyamide reverse osmosis composite membrane according to claim 1, characterized in that: In step (2), silicate, aluminate, titanate, zirconate compounds and monomer trimesoyl chloride are dissolved in a solution of a xylene-n-hexane mixed solvent, with the ester compound content being 0-0.2 wt%, preferably 0.001-0.5 wt%, and more preferably 0.005-0.15 wt%.

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